1. Field of the Invention
The present invention relates to a field emission device, and more particularly, to a field emission device comprising a field emission suppressing gate for suppressing electron emission which is interposed between a cathode and a field emission inducing gate.
2. Discussion of Related Art
Field emission devices have been widely used as an electron source of a microwave element, a sensor, a flat panel display, or the like, which emits electrons from a cathode electrode when an electric field is applied to the same in a vacuum or a specific gas atmosphere.
Efficiency of electron emission significantly depends on an element structure, an emitter material, and an emitter shape in the field emission device. At present, the structure of the field emission device is mainly classified into a diode type consisting of a cathode and an anode, and a triode type consisting of a cathode, a gate, and an anode.
The cathode or electric field emitter acts to emit electrons, the gate acts to induce electron emission, and the anode receives the emitted electrons in the triode type field emission device. Since the electric field for electron emission is applied to the gate adjacent to the emitter in the triode type structure, the field emission device may be driven at a low voltage and emission current may be readily controlled as compared to the diode type structure, as a result of the triode type is being actively developed.
Material used for the electric field emitter may include metal, silicon, diamond, diamond like carbon, carbon nanotube, carbon nanofiber, etc., the carbon nanotube and nanofiber are thin and pointed, and stable in themselves, so that they are widely used for the emitter material.
Hereinafter, a Spindt-type field emission device, which is one of the structures widely used among conventional field emission devices, will be described. FIG. 1 is a diagram illustrating a schematic configuration of a Spindt-type field emission device in accordance with the related art.
The Spindt-type field emission device consists of a cathode, a gate, and an anode. The cathode is comprised of a cathode substrate 11, a cathode electrode 12 formed on the cathode substrate, a metal tip 13 with an insulator 21 surrounding the metal tip 13 and having an internal gate opening 22, and a gate electrode 23 formed on the insulator 21. An anode electrode 32 is formed on an anode substrate 31, which is arranged to face the above-mentioned whole cathode and gate structure.
In order to fabricate such a field emission device, the gate opening 22 is formed to have a thickness of about 1 um on the insulator 21 and a sacrificial isolation layer is formed on top of that. Electron beam evaporation is performed to thereby form a self-aligned metal tip 13.
Thus, while a fine pattern should be formed and a self-alignment scheme by means of electron beam evaporation should be performed in the above-mentioned procedure, there is difficulty in application of such a field emission device for implementing a large area display.
Efforts to fabricate the field emission device with a more simplified process have been made to cope with such problem, and the carbon nanotube and carbon nanofiber among electric field emitter materials have been used to meet these efforts.
The carbon nanotube and carbon nanofiber have very small diameters, on the order of nanometer, in themselves while having a long length, on the order of micrometer, so that they are highly suitable for an electron emission source. However, when they are used as the electron emission source by means of an electric field, it is not easy to form a self-aligned electron emitting gate so as to have a structure capable of readily inducing and controlling electron emissions compared to the Spindt-type metal tip of FIG. 1.
FIG. 2 is a diagram illustrating a schematic configuration of a field emission device for a carbon nanotube or carbon nanofiber in accordance with the related art. FIG. 2 differs from FIG. 1 in that the carbon nanotube or carbon nanofiber used for the electric field emitter 14 of the field emission device of FIG. 2 is exposed through a gate opening with a length of 10 um formed within an insulator.
Thus, the emitted electrons flow into the gate to result in a leakage current. In addition, the gate opening is larger compared to the thickness of the insulator, which causes difficulty in controlling electron emission due to an anode voltage, and causes the emitted electron beam to be widely spread when it reaches the anode as compared to its emitting instance.
These phenomena deteriorate the properties of the field emission device, and in particular, they may cause a significant problem when the field emission device is applied for a flat panel display.